The present invention relates generally to a sensing surface, or focal plane, for an infrared camera. More particularly, the present invention relates to a hybrid focal plane array formed of densely packed, self guarded Schottky infrared internal emission photodiodes.
In U.S. Pat. No. 3,902,066, issued Aug. 26, 1975 to Roosild et al, there is described a monolithic Schottky barrier array for detecting the infrared portion of the electromagnetic spectrum. Individual Schottky electrodes within the array are connected through enhancement mode field effect transistors to charge coupled devices for providing signals to an infrared vidicon camera. The performance of this array has proven to be limited by aliasing and drop-out effects which are related to the low percentage active area of the array. Space is required within the focal plane for multiplexing the signals derived from the individual Schottky electrodes, and also for the guard rings which are provided about each individual Schottky electrode. In such an array, the charge coupled device signal readout circuitry occupies up to 50% of the focal plane area. Add to this the losses of sensing area because of guard rings and channel stops and the active area of the array is reduced to approximately 30 to 45 percent of the total area of the array.
An improvement has been made upon the aforementioned prior art array by Charlotte E. Ludington, a coinventor in the present patent application, and a separate patent application entitled "Hybrid Schottky Infrared Focal Plane Array," bearing Ser. No. 455,715, has been filed thereon. The Ludington patent application discloses a design for an infrared internal emission Schottky array that is compatible with hybrid bump bonding techniques as known in the prior art and shown, for example, in U.S. Pat. No. 3,808,435 issued to Robert T. Bate et al. This structure increases the active area of the array to about 70% of the total area but still leaves blind spots in the array because of the areas occupied by the guard rings which surround the individual Schottky cells.